The present embodiments relate to a vertical movement device for an examining table.
The examining tables for high-end magnetic resonance imaging medical diagnosis systems may include vertical lifting/lowering functions, and in view of the different weights of subjects to be examined, the tables may be able to lift a relatively large working weight (e.g., >250 kg or >300 kg), so as to meet different operation requirements. The tables may also have a relatively high vertical moving speed (e.g., >35 mm/s) to reduce the examination time. Furthermore, such vertical movement structures may have self-locking functions to ensure the safety of the subjects to be examined.
A transmission mechanism set may be used to accomplish such a heavy-load, high-speed vertical movement with the self-locking function, and the transmission mechanism may have a relatively high transmission efficiency to make the examining table reach the magnet's examination height as quickly as possible. The self-locking function for stability would sacrifice the transmission efficiency, and a low transmission efficiency, in turn, would lead to an increase in noise (e.g., up to 65-70 dBA). In a medical diagnosis system, noises may make the subjects examined feel nervous and anxious, which is disadvantageous to high quality accurate diagnosis.
FIG. 1 is an isometric view of a vertical movement structure for an examining table of the prior art. As shown in the figure, a central zone for medical examination is provided in the middle of a magnet 50, and an examining table 51 can enter or exit the central zone along a horizontal direction as indicated by arrow H. The end of the examining table close to the magnet 50 may be the front end of the examining table, and the end of the examining table away from the magnet 50 may be the back end of the examining table. A driving motor 52 is may be provided near the back end of the examining table 51, a driving wheel 53 is disposed on the output shaft of the driving motor 52, and a synchronization belt 54 is wound around and between the driving wheel 53 and a driven wheel 55. The driven wheel 55 is also disposed on the examining table 51, and the rotation axis of the driven wheel 55 is parallel to the rotation axis of the driving wheel 53.
FIG. 2 shows a locally enlarged isometric view of the parts marked as number 2 in FIG. 1. In order to clearly show the transmission structure, some structures such as, for example, the synchronization belt are not shown in FIG. 2. As shown in FIG. 2, the rotation of the driven wheel 55 rotates a worm 56 that is carried coaxially with the driven wheel. The worm 56 rotates a worm wheel 57 that is engaged with the worm 56. The rotation direction of the worm wheel 57 is perpendicular to the rotation direction of the worm 56.
Referring again to FIG. 1, the worm wheel 57 is connected to a nut 58. When the worm wheel 57 rotates, the nut 58 rotates with the worm wheel 57, and at the same time, the nut 58 moves on a screw 59 (e.g., the screw 59 being fixed on a base 40). The nut 58 moves on the screw 59 along the direction indicated by arrow V in FIG. 1, so as to carry the examining table 51 and move the examining table 51 vertically.
When using this transmission mechanism set, the transmission efficiency and the self-locking function of the worm wheel 57 and the worm 56 restrict each other. Thus, improving the transmission efficiency of the worm wheel 57 and the worm 56 leads to a reduction of the self-locking performance of the worm wheel 57 and the worm 56. Currently, the overall transmission efficiency of such a transmission mechanism set is approximately 26%, and the low transmission efficiency is one of the reasons for loud noises. The maximum lifting weight of the structure shown in FIG. 1 is approximately 200 kg, and a larger lifting weight may cause a motor power overload, also increasing the noise significantly. The nut 58 and the screw 59 also need a higher transmission efficiency to meet the requirements of the moving speed of the examining table, which requires the screw 59 to have more thread heads (e.g., up to seven thread heads). The above situation makes the manufacturing of the vertical movement device for an examining table more difficult, the precision requirements stricter and the manufacturing costs higher.